Conduit with heated wick

ABSTRACT

A conduit for a breathing circuit includes a heater associated, at least in part, with a portion of hydrophilic material. The purpose of the heater is to evaporate any condensed liquid collecting in the conduit, which is first sucked up by the hydrophilic material. The heated wick reduces the risk of collected water being passed to the patient and causing choking fits or discomfit. It is preferred that the heated wick lies freely in the conduit to settle at low-points in the conduit where condensation may collect.

BACKGROUND TO THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to conduits and in particular toconduits for use in a breathing circuit.

[0003] 2. Summary of the Prior Art

[0004] In assisted breathing, particularly in medical applications,gases having high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Build up ofcondensation on the inside wall of the conduit is a frequent result ofthis high humidity. In the prior art, attempts have been made to reducethe adverse effect of this condensation by either reducing the level ofcondensation or providing collection points in the conduit for drainingcondensed liquid from the conduit. Reducing the condensation hasgenerally been by maintaining or elevating the temperature of the gasesflow and/or of the conduit wall to reduce the formation of condensation.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide a conduit,which will at least go some way towards improving on the above or whichwill at least provide the public and the medical profession with auseful choice.

[0006] In a first aspect the invention consists in a conduit for abreathing circuit including heating means located within said conduitand associated, at least in part with a portion of hydrophilic material,there being no means for direct supply of water or fluid to saidhydrophilic material from outside said conduit.

[0007] In s second aspect the invention consists in a breathing circuitincluding an expiratory gases flow path and a heating means locatedwithin said expiratory gases flow path and associated at least in partwith a portion of hydrophilic material.

[0008] To those skilled in the art to which the invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the scope of the invention as defined in the appended claims. Thedisclosures and the descriptions herein are purely illustrative and arenot intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a cross sectional elevation of a conduit for theexpiratory limb of a breathing circuit according to the presentinvention.

[0010]FIG. 2 is a cross sectional view of a section of conduit wallaccording to one possible construction.

[0011]FIG. 3 is a cross sectional view of a co extrusion die head forextruding a conduit including two longitudinal strips of permeablematerial, similar to the conduit of FIG. 1.

[0012]FIG. 4 is a cross sectional elevation of a coaxial breathingcircuit according to a further embodiment of the present inventionincorporating a heated wick in the expiratory gases flow path.

[0013]FIG. 5 is a side elevation in partial cross section of a coaxialbreathing circuit including a heated wick in both the inspiratory andexpiratory gases flow paths.

[0014]FIG. 6 is a representation of a breathing circuit with anexpiratory limb fashioned according to the present invention andincluding a heated wick according to a further aspect of the presentinvention.

[0015]FIG. 7 is a cut-away perspective view of a heated wick accordingto a further aspect of the present invention

[0016]FIG. 8 is a side elevation partially in cross section of anexpiratory limb conduit according to a further embodiment of the presentinvention.

DETAILED DESCRIPTION

[0017] The present invention involves the provision of a heated wickwithin one of the lengths of conduit making up a breathing circuit. Byheated wick we refer to a heater associated with a portion ofhydrophilic material. The heated wick is disposed freely within theconduit so that at least part of it lays in low points of the conduit atwhich condensation accumulates. Accumulated condensation is absorbed bythe hydrophilic material and re-evaporated by heat from the heater.

[0018] As seen in FIGS. 1A and 7 the heated wick 100 is comprised of anouter hydrophilic material 108 covering an inner insulating hydrophobiclayer 112 which in turn covers a heater element 110. Any water thatcollects in the conduit 102 is attracted to and drawn into thehydrophilic material 108, and is then re-vaporised as it is heated bythe heater element 110. The intermediate hydrophobic insulating layer112 is provided to electrically insulate the inner heater element 110from the rest of the system.

[0019] Such a heated wick 100 as shown in FIG. 7 may be constructed byco-extruding the hydrophobic insulating layer 112 and hydrophilic layer108 onto the heater wire 110. Suitable materials for the hydrophiliclayer include polyester or polyurethane foam, or a braid of hydrophilicmaterial e.g. cotton. Suitable materials for the hydrophobic layerinclude polypropylene or silicone coatings.

[0020] An alternate form for the heated wick is shown in each of FIGS.1b, 1 c and 1 d. In FIG. 1b the heated wick includes a looped backheater element 110, coated in a hydrophobic insulating layer 112, andthe whole encased within a hydrophilic surrounding layer 108. In afurther variation depicted in FIG. 1c the heater element is anelectrical resistance heater and includes a length 120 of higherresistance and a length 121 of lower resistance, insulated from oneanother and joined at their remote ends. In a still further variationdepicted in FIG. 1d the heated wick 100 is disposed in the conduit as asimple loop. Each of these variations is provides both ends of theheated wick at the same end of the conduit, allowing a single connectionof the heater element to an energising source. The embodiment of FIG. 1chas the additional advantage that the heater element voltage at theremote end will be lower than half the supply voltage, and withappropriate selection can be very close to zero.

[0021] The heated wick may also be provided in both the inspiratory andexpiratory conduits. In this case a single length of heated wick may rundown the inspiratory conduit and back up the expiratory conduit, withthe ends of the conduits being insufficiently close proximity to enableeasy electrical connection to both ends.

[0022] The heated wick is provided with connections at its ends forconnecting to an energising source. The ends of the wick may be directlyelectrically connected to electrical connectors in the connector of thetube or conduit. These connectors may for example be a socket forreceiving a plug from a voltage source. Alternatively the heated wickmay be a fixture of an assisted breathing device, such as a ventilatoror humidifier, and may extend from within the breathing conduitconnection port of the device, or be plugged into a socket within suchport. Many other configurations for supplying power to the heated wickwill also suggest themselves.

[0023] The heater element 110 is also effective to supply heat to thegases stream to reduce the overall level of condensation occurringwithin the conduit. At the same time any condensation that does occur issucked up by the wick and reevaporated by heat from the heater element110. Accordingly where a heated wick is provided in the inspiratory armof the breathing circuit humidity supplied to the gases stream prior toentry into the breathing circuit is not lost through condensation,instead being re-evaporated by the heated wick. This reduces the totalhumidification load of the breathing circuit as well as eliminating therequirement for conduit drainage ports.

[0024] Where the heated wick is provided in the expiratory conduit iteliminates the need for conduit drainage ports. Furthermore it providesadditional advantages when used in conjunction with an expiratoryconduit in which at least a part of the conduit wall is formed from abreathable material. Such an arrangement is shown in FIG. 6.

[0025] A breathable material, as used herein, is a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases. Materials may be breathable due to theircomposition, physical structure a combination thereof.

[0026] One such breathable material is an activated perfluorinatedpolymer material having extreme hydrophilic properties. An example ofthis polymer material is marketed under the trade mark NAFION by DuPontFluoro products of Fayetteville USA. This material is usefull due to itsextreme hydrophilic properties and due to its ability to be extruded,particularly to be co-extruded in combination with other plasticmaterials

[0027] Alternative materials are also envisaged including:

[0028] (a) Hydrophilic thermoplastics,

[0029] (b) woven treated fabric products exhibiting breathablecharacteristics

[0030] The preferred material is a hydrophilic polyester block copolymerformed into a homogeneous flat film. An example of such a film is soldunder the brand SYMPATEX. This material is particularly suited to thinfilm productions.

[0031] An example of application of the conduit with heated wick isshown in FIG. 6. A heater element 110 coated with a hydrophilicmaterial, runs the length of the semi-permeable conduit 102 and theinspiratory conduit 101. During operation humidified gases are drawnthrough inspiratory conduit 101, then flow through the T connector 103,and are then delivered to the patient (not shown). When the patientexpires the gases flow through the T connector 103, and then flowthrough the breathable expiratory conduit 102. The expiratory gases willbe almost saturated with humidity and as the wall of the breathableexpiratory conduit 102 will be relatively cool, some portion of thevapour in the gases will condense and therefore water will collect inthe conduit and run towards the lowest point 106. As already mentionedsuch collection of water is undesirable and therefore the heated wick100 is provided to revaporise the water that collects. This isparticularly important where the breathable material is one, such asSYMPATEX, which transmits water vapour but does not transmit liquidwater. Wile such materials are advantageous for their ability to stopharmful bacteria and viruses this advantage is offset by their inabilityto transmit liquid water. By re-evaporation of any collected water bythe heated wick it can be transmitted through the breathable membrane inits vapour state.

[0032] Referring to FIG. 1, in one embodiment, the conduit 4 of theexpiratory limb of a breathing circuit is formed having one or morelongitudinal strips 2, 3 of semi permeable membrane as part of the wall1 thereof.

[0033] Referring to FIG. 8 an alternative embodiment of the expiratorylimb conduit is shown in which the entire flexible wall membrane of theconduit is formed from a breathable plastic membrane, extruded and woundhelically with edges of adjacent turns sealed to one another.

[0034] Referring to FIGS. 4 and 5, further aspects is shown in which anexpiratory limb conduit according to the present invention is providedas a gases flow path of a coaxial conduit configuration, such thatexpiratory gases and inspiratory gases each flow in one of the innerconduit or the space between the inner conduit and the outer conduit andin use water vapour but not liquid water is transmitted from theexpiratory gases passageway to the inspiratory gases passageway.

[0035] Referring to FIGS. 2 & 8, spiral or helical internal (orexternal) reinforcing members 30, or a series of annular hoopreinforcing members, may be provided outside (or inside) the tubularmembrane 6 to provide support to it. The helical, spiral or hoopsupporting members may for example be formed from polymer plasticmaterials, such as the material used in the wall of the conduit (notbeing the semi permeable regions), or alternatively may for example be ametal wire support, such as drawn steel wire.

[0036] The conduit shown in FIG. 2 may be formed in any one of a numberof methods. For example the tubular membrane 6 may be supplied in acontinuous tube. Alternatively it might be supplied in tape form, whichmay result in the conduit of FIG. 8. Supplied as extruded tape 81, themembrane may be wound helically onto a former. The helical supportingrib 30, provided in a semi molten state is then laid on the overlapbetween adjacent turns. The heat from the helical supporting rib 30bonds the two adjacent strips with itself forming a flexible resilientconduit once cooled.

[0037] Referring to FIG. 8 an additional longitudinal reinforcement maybe provided to alleviate the shortcomings of some of the breathablematerials. This reinforcement may be in the form of a plurality ofreinforcing threads 83. The threads 83 run parallel to the length of theconduit and are supported on the helical reinforcing ribs, spanningbetween them. As many threads may be provided. For example eight threadsmay be spaced around the circumference of the tube. The reinforcingthreads 83stop accidental stretching of the conduit, and providing theyhave some stiffness and the rib spacing is not to large, also reduce anylongitudinal compression of the conduit under negative relative internalpressures.

[0038] Referring to FIG. 3 the conduit, such as that shown in FIG. 1,may alternatively be formed by co extrusion of the semi permeablematerial (where the material is a suitable extrudable material) with aplastic material forming the remainder of the conduit wall. A suitableco extrusion die 9 is depicted in FIG. 3 in which a pair ofcircumferential sections 7 of the die opening have the semi permeableplastic material extruded therethrough, and the remainder sections 8 ofthe annular extrusion opening have the non permeable plastic wallmaterial extruded therethrough.

[0039] The purpose of the breathable region or regions of the conduitwall is to allow diffusion of water vapour (and for some materialsliquid water) from the expiratory limb of the breathing circuit alongthe path thereof independent of specific drain locations This eliminatesthe build up of condensation within the expiratory limb by drying thehumidified gases during their flow through the expiratory limb. Thisfurthermore reduces the humidity of the gases arriving at ancillaryequipment, such as filters, ventilators and the like reducing the riskof condensation accumulation, thereby improving their operation.

[0040] In accordance with a further aspect of the invention, and asexemplified in FIGS. 4 and 5 the conduit incorporating one or morelongitudinal strips of semi permeable membrane may further beincorporated in a coaxial breathing circuit as a passive humidificationdevice. In particular referring to the cross section in FIG. 4 thecoaxial breathing circuit may include an outer conduit 11 and an innerconduit 10. Preferably, for heat transfer reasons, the inner conduit 10carries the inspiratory flow in the space 12 there within. Theexpiratory flow is carried in the space 13 between the inner conduit 10and the outer conduit 11, and a doubled back heated wick 100 is providedin the expiratory flow space. The airflow configuration is indicated byarrows 20, 19 respectively in FIG. 5.

[0041] The inner conduit 10 is formed having one or more longitudinalstrips 2, 3 of semi permeable membrane in the wall 1 thereof, as haspreviously been described with reference to FIGS. 1, 2 and 3. Thushumidity in the expiratory flow space 13 may pass through the sections2, 3 of semi permeable membrane to humidify the inspiratory flow ininspiratory flow space 12.

[0042] The semi permeable membrane works on relative partial pressuresof water vapour so, with the flows in a counter flow arrangementsubstantial passive humidification of the inspiratory flow can beachieved

[0043] Referring to FIG. 5 a circuit configuration including the coaxialconduit depicted in FIG. 4 is represented, but with a heated wick 100disposed in both of the inspiratory and expiratory flow parts (forexample doubling back at the patient end connector 15. In this circuitthe conduit has a patient end connector 15 and a ventilator endconnector 16 having inspiratory port 17 and an expiratory port 18. Theinspiratory 20 and expiratory 19 counter flows are indicated.

[0044] So in its broadest form the invention is a conduit for abreathing circuit which includes a heater associated, at least in partwith a portion of hydrophilic material. The purpose of the heater is toevaporate any condensed liquid collecting in the conduit. The heatedwick is not a humidifier and so no liquid is supplied directly to thehydrophilic material from outside said conduit. The heated wick reducesthe risk of collected water being passed to the patient and causingchoking fits or discomfit. It also improves the predictability of thehumidity levels in the gases passed to the patient. It is preferred thatthe heated wick lies freely in the conduit to settle at low points inthe conduit where condensation may collect.

[0045] Where the conduit in question is an expiratory conduit, or atleast where the heated wick is located in an expiratory flow path of abreathing circuit, then the heated wick will have additional benefitswhere the conduit has at least of potion of its wall formed frombreathable material for passive dehumidification of the expired gases.Because the breathable material will pass only vapour, evaporation ofany condensed liquid within the conduit will allow that liquid tosubsequently be passed.

[0046] Another aspect to the invention is the construction of the heatedwick, which is preferably an elongate heating element covered with aninner hydrophobic insulating layer co-extruded with an outer hydrophiliclayer.

[0047] It will be appreciated that the concepts encapsulated by thedescribed and illustrated embodiments are not restricted to beingcombined only as described. For example the heated wick described withreference to FIGS. 6 and 7 may be used in the coaxial conduit of FIGS. 4and 5 or the separate limbed conduit as in FIG. 6. Similarly the conduitincorporating the breathable membrane, whether it be the inner conduitof the coaxial configuration shown in FIGS. 4 and 5 or the stand aloneexpiratory limb of FIG. 6, may be formed as a co-extrusion as in FIGS. 1and 3 or as an extruded tape as in FIG. 8 and with the breathablemembrane being of a number of alternate materials. While someembodiments have been described as preferred and convey particularadvantages over other embodiments many other combinations may provecommercially useful.

1. A conduit for a breathing circuit including heating means locatedwithin said conduit and associated, at least in part with a portion ofhydrophilic material, there being no means for direct supply of water orfluid to said hydrophilic material from outside said conduit.
 2. Aconduit as claimed in claim 1 wherein said heating means comprises anelongate heating element covered with an inner hydrophobic insulatinglayer and an outer hydrophilic layer.
 3. A conduit as claimed in claim 1wherein said heating means lies freely in said conduit to settle over atleast some of its length at low points in said conduit where condensedwater vapour may collect.
 4. A conduit as claimed in claim 2 whereinsaid heating means lies freely in said conduit to settle over at leastsome of its length at low points in said conduit where condensed watervapour may collect.
 5. A conduit as claimed in any one of claim 1wherein said conduit is an expiratory conduit and said heating means islocated in an expiratory flow path of said conduit and at least a lengthof said conduit has a conduit wall wherein at least a region of saidconduit wall is of a breathable material.
 6. A conduit as claimed inclaim 5 wherein said at least a region is or are distributed over saidlength of said conduit.
 7. A conduit as claimed in any one of claim 2wherein said conduit is an expiratory conduit and said heating means islocated in an expiratory flow path of said conduit and at least a lengthof said conduit has a conduit wall wherein at least a region of saidconduit wall is of a breathable material.
 8. A conduit as claimed inclaim 7 wherein said at least a region is or are distributed over saidlength of said conduit.
 9. A conduit as claimed in any one of claim 3wherein said conduit is an expiratory conduit and said heating means islocated in an expiratory flow path of said conduit and at least a lengthof said conduit has a conduit wall wherein at least a region of saidconduit wall is of a breathable material.
 10. A breathing circuitincluding an expiratory gases flow path and a heating means locatedwithin said expiratory gases flow path and associated at least in partwith a portion of hydrophilic material.
 11. A breathing circuit asclaimed in claim 10 said heating means comprises an elongate heatingelement covered with an inner hydrophobic insulating layer and an outerhydrophilic layer.
 12. A breathing circuit as claimed in claim 10wherein said heating means lies freely in said conduit to settle over atleast some of its length over low points in said conduit where condensedwater vapour may collect.
 13. A breathing circuit as claimed in claim 11wherein said heating means lies freely in said conduit to settle over atleast some of its length over low points in said conduit where condensedwater vapour may collect.
 14. A breathing circuit as claimed in any oneof claims 10 to 13 wherein said expiratory gases flow passage is definedby at least one conduit wall and at least a region of said conduit wallis of a breathable material.
 15. A breathing circuit as claimed in anyone of claim 14 wherein said breathing circuit is a coaxial breathingcircuit including an inner conduit and an outer conduit, the innerconduit located within the outer conduit, such that one of aninspiratory or expiratory flow path are provided within the innerconduit and the other of the inspiratory or expiratory flow paths isprovided between the inner conduit and the outer conduit and at least aregion of the wall of said inner conduit is of a breathable material.